1. Field of the Invention
The present invention relates to an image processing apparatus, and more particularly to an image processing apparatus for decoding compressed image information obtained from a transmission channel or a recording medium.
2. Related Background Art
In a still image transmission system, an image is compression encoded on the transmitter side, then transmitted through a transmission channel such as a satellite channel, a public channel, a recording/reproducing circuit of an image record/reproducing system or a digital record/reproducing system, to a receiver side, and is decoded there to reproduce the original image.
The transmitter side selects necessary parts from image data entered, for example, from an image scanner or a video camera, effects image processing such as image enlargement or reduction or deformation, further effects data compression by sub-sampling and DPCM, and sends the obtained compressed data in a predetermined format to the transmission channel. The receiver side usually has plural frame memories, and reproduces the original image by expanding the signals received from the transmission channel, utilizing said frame memories cyclically. Then the data in a frame memory, storing the restored image, are read for display. Thus, while decoding (expansion) is conducted on the contents of one frame memory, the restored image data are read from another frame memory for display. The display of the received image on monitor has to wait during the decoding if only one frame memory is available, but the alternate or cyclic use of plural frame memories allows one to reduce the waiting time for image display.
In a case where there are provided plural, for example two, frame memories as explained above, it is possible to synthesize a part of the image stored in the first frame memory with a part of the image stored in the second frame memory, by replacing a part of the image data read from said first frame memory with the image data read from the second frame memory. However, such synthesized image data themselves are not stored in the first frame memory, nor in the second one, so that it has not been possible to apply image processing to such synthesized image.